1. Field of the Invention
This invention relates to an image processor performing the processing of image data and an image forming apparatus including the image processor.
2. Description of the Related Art
Conventionally, an output of digital image data to a printer for example has been achieved by a halftone processing by which color values showing the tones of the respective display colors of the respective pixels are converted from multivalued data represented by a plurality of bits to binary data represented by 1 bit. In this halftone processing, one method to express the original image with a high image quality is an error diffusion algorithm. In the error diffusion algorithm, an error (difference) from the original multivalued data caused by the binarization of the respective color values is distributed to the surrounding pixels at a predetermined rate and is added to the color value of the same color for diffusion, thereby preventing reduced information amount.
In the halftone processing by this error diffusion algorithm, in order to calculate a value to be added to the color value of each pixel, the value must be stored in a memory as an intermediate value. A circuit, not only for the halftone processing but for other image processing using such an intermediate value, tends to become complicated, causing a longer processing time. Thus, in order to provide an image processing having a higher speed, Patent Publication 1 (Japanese Patent Laid-Open Publication No. H6-266324) for example discloses a technique according to which a plurality of image processing units are provided to the data of a plurality of scan lines so that the processing is carried out in a parallel manner for a higher speed.
On the other hand, depending on image data, it may be preferred to handle each data obtained by setting a plurality of predetermined pieces of pixel data respectively continuing in the main scan direction and the sub scan direction as a packing (hereinafter referred to as packing data). For example, in the case of image data that is subjected to a pixel number conversion processing for a high image quality, an image processing may be performed in such a manner that the respective pieces of pixel data packed based on the pixel range prior to the pixel number conversion are handled collectively, for a simpler handling.
However, there has been a disadvantage conventionally, that a long time is required to rearrange the respective pieces of packed pixel data according to the respective scan lines to input the packed pixel data to an image processing unit. Furthermore, when such packing data is used as input data in the halftone processing by the error diffusion algorithm, a disadvantage is caused where a processing becomes complicated or a high-speed processing cannot be provided effectively for example, by executing a processing while obtaining pixel data for the respective scan lines.